docs: def format(self, record):
          """
          Format a log record to JSON, if the message is a dict
          assume an empty message and use the dict as additional
          fields.
          """
  
          fields = record.__dict__.copy()
  
          if isinstance(record.msg, dict):
              fields.update(record.msg)
              fields.pop('msg')
              msg = ""
          else:
              msg = record.getMessage()
  
          try:
              msg = msg.format(**fields)
          except (KeyError, IndexError, ValueError):
              pass
          except:
              # in case we can not format the msg properly we log it as is instead of crashing
              msg = msg
  
          if 'msg' in fields:
              fields.pop('msg')
  
          if 'exc_info' in fields:
              if fields['exc_info']:
                  formatted = tb.format_exception(*fields['exc_info'])
                  fields['exception'] = formatted
              fields.pop('exc_info')
  
          if 'exc_text' in fields and not fields['exc_text']:
              fields.pop('exc_text')
  
          logr = self.defaults.copy()
  
          logr.update({'@message': msg,
                       '@timestamp': datetime.datetime.utcnow().strftime('%Y-%m-%dT%H:%M:%S.%fZ'),
                       '@source_host': self.source_host,
                       '@fields': self._build_fields(logr, fields)})
  
          return json.dumps(logr, default=self.json_default, cls=self.json_cls)